Ball point pen tip and production method thereof

ABSTRACT

A method of manufacturing a ball point pen tip comprises providing a body member having a distal end portion and a ball holding portion and disposing a ball in the ball holding portion. Caulked portions having different angles are formed throughout the entire periphery of an outer surface of the distal end portion of the body member using a caulking tool while bringing a pressure contact portion of the caulking tool into contact with the ball.

BACKGROUND OF THE INVENTION

This invention relates to a ball point pen tip having the structurewherein a reduced diameter portion is formed by caulking inward a distalbutt end portion of a taper surface whose diameter progressivelydecreases towards a distal end, and a ball as a writing member isallowed to partly protrude from an opening while being held by a ballholding portion as a part of an ink passage, and to a production methodof such a ball point pen tip.

BACKGROUND INFORMATION

Ball point pens have been designed conventionally so that writing can bemade mainly at a writing angle within the range of 90° to 50°. However,there is the case where writing is made at a smaller writing angle thanthe ordinary writing angle when Arabic characters or alphabets arewritten, and ball point pens capable of providing clear writtencharacters even at such a small writing angle have been desired.

To attain writing at the small writing angle, the distal butt endportion of a ball point pen tip must not catch the surface of ato-be-written object such as a sheet of paper. This requirement can besatisfied by preventing the distal end portion of the ball point pen tipother than the ball from coming into contact with a written surface evenwhen writing is made at a small writing angle. To prevent the contact ofthe distal end portion of the ball point pen tip with the writtensurface, it may be possible to set a caulking angle of a reduceddiameter portion, which prevents fall-out of the ball, to a small angle,or to reduce the thickness of the distal end portion of the ball pointpen tip. However, when the thickness of the distal end portion isreduced or the caulking angle of the distal butt end portion is set to asmall caulking angle, machining with a large deformation quantity mustbe carried out in comparison with the case where machining is made at alarge caulking angle, in order to obtain a diameter reduction quantitynecessary for holding the ball. In this case, adverse influences areexerted on the inner surface of the reduced diameter portion as aportion corresponding to the caulked portion of an ink passage and theshape of the distal butt end is likely to become non-uniform. Inconsequence, uniform supply of ink to the written surface or uniformrotation of the ball is impeded and a non-uniform density occurs inwritten characters. When the distal end shapes of the butt end are notuniform, a portion which is unnecessarily elongated than required isformed towards the distal end side, and the ball is likely to come intocontact with the written surface at a small writing angle.

From the aspect of production methods, a production method of a ballpoint pen tip is known which comprises forming interior components of aball point pen tip such as a center hole, a ball chamber, etc, so as tohold a ball of the metallic ball point pen tip made of a metal such asbrass, german silver, stainless steel, copper alloy and aluminum alloy,loading then the ball into the ball chamber and caulking inward a distalbutt end portion so as to hold the ball. The caulked portion formed atthe distal butt end portion for holding the ball greatly affects writingquality of the ball point pen such as a hand writing condition and catchwith a sheet surface.

This caulking working of the ball point pen tip is effected by bringinga pressure contact member into pressure contact with the ball point pentip, and ball point pen tips having various required quality have beenworked by adjusting the angle at which the pressure contact surface ofthe pressure contact member comes into contact with the ball point pentip (caulking angle).

When the caulking angle of the ball point pen tip and its caulkingstrength can be variously adjusted, variance of the angle and size ofthe caulked portion occurs in the product, and in order to keep requiredwriting quality, strict check of defective products and strict controlof the caulking angle must be made. In either case, job becomes morecomplicated.

Particularly in the case of the ball point pen tips where at least two,or a plurality of, stages of caulked portions having different anglesare formed, some of the production methods according to the prior artgenerate non-uniform thickness portions at the boundary portions of aplurality of caulked portions having different angles due to elongationof the tip material caused by the caulking work, as typified byprojections and fins, and these non-uniform portions catch the sheetsurface and blank portions where ink is not applied occur inhand-written characters.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved ballpoint pen tip which completely obviates the drawbacks with the prior artdescribed above.

It is another object of the present invention to provide a novelproduction method of a ball point pen tip.

The ball point pen tip according to the first embodiment of the presentinvention has the following structure. Namely, (1) the angle definedbetween a tangent coming into contact with a ball and with a ball pointpen tip and a center line of the ball point pen tip is within the rangeof 3020 to 50°, (2) corner portions formed by caulking the ball pointpen tip (boundary line between the portion with which a caulking toolcomes into contact and the portions with which it does not) and cornerportions at the foremost tip portion of the ball point pen tip exist atportions other than portions in contact with the tangent of the ballpoint pen described above, and (3) the length of a portion (ink controlportion) formed when a part near the opening of the inner surface of theball point pen tip comes into pressure contact with the ball, in thelongitudinal direction, is 15 to 35% of the diameter of the ball fromthe end of the opening during caulking.

In a ball point pen tip of the type wherein a butt end portion at adistal end portion of a taper surface the diameter of whichprogressively decreases towards the distal end is caulked inward in sucha manner as to form a reduced diameter portion and a ball as a writingmember is held by a ball holding portion as a part of an ink passage insuch a manner that a part of the ball protrudes from an opening, theball point pen tip according to another embodiment of the presentinvention has the construction wherein the reduced diameter portioncomprises first and second caulked portions having mutually differentcaulking angles, and a caulking angle α of the first caulked portion onthe distal butt end side, a caulking angle β of the second caulkedportion, the diameter reduction angle γ of the taper surface, thediameter D of the ball, the projection height h of the ball from theopening and the distance t between the outer shape of the distal buttend portion at the opening and the outer shape of the ball satisfy thefollowing relations (1) to (4):

    0.25≦h≦0.35D                                 (1)

    0.007 mm≦t≦0.030 mm                          (2)

    γ+10°≦β≦γ+40° (3)

    β+10°≦α≦β+40°  (4)

To prevent the butt end of the ball point pen tip from coming intocontact with the written surface even at a small writing angle, the ballprojection height (h), the distance (t) between the outer shape of thedistal butt end portion in the opening and the outer shape of the ball,and the caulking angle should be adjusted. The value (t) which preventsat least the distal butt end portion of the ball point pen tip at theopening from coming into contact with the written surface changes inaccordance with the writing angle (θ), the ball diameter (D) and theball height (h). The distance (t) between the outer shape of the distalbutt end portion at the opening and the outer shape of the ball can beexpressed by the writing angle (θ), the ball diameter (D) and the ballprojection height (h) as the following formula (5). Incidentally, theterm "writing angle (θ)" represents the minimum desired writing angleamong the angles defined between the longitudinal direction of thewriting instrument and the written surface: ##EQU1##

The formation of the reduced diameter portion by caulking the distalbutt end portion of the ball point pen tip means and provides not onlythe prevention of fall-off of the ball but also the formation of an inksupply control portion on the inner wall of the ball holding portion.This ink supply control portion regulates the push force of the caulkingworking, brings the ball into contact with the inner wall of the ballholding portion and forms a smooth portion around a part of the innerwall of the ball holding portion having a uniform clearance from theball. This portion makes transfer of ink to the ball surface uniform andeasy and supplies uniformly ink transferred to the ball to the writtensurface. (Hereinafter, the smooth portion formed around the inner wallof the ball holding portion and having a uniform clearance from the ballwill be referred to as the "ink control portion".)

In other words, because the ink control portion is formed, writtencharacters which are least affected by the writing direction and thewriting angle and have a uniform density can be obtained. As a result ofintensive studies, the inventors of the present invention have found outthat written characters having a uniform density can be obtained withthe minimum influences of the writing direction and the writing angle ofthe ink control portion, and the uniform formation of the shape of thedistal end portion of the ball point pen tip is greatly affected by thecaulking angle of the distal butt end portion of the ball point pen tip,and have thus succeeded in obtaining the ball point pen tip which isfree from catch with the written surface even at a small writing angleand can obtain beautiful characters having a uniform density.

In a production method of a ball point pen tip for forming a pluralityof caulked portions having different angles on the outer surface of thedistal butt end portion of a metallic ball point pen tip throughout thefull periphery for holding the ball, the production method of the ballpoint pen tip according to the present invention comprises bringing apressure contact portion of a caulking tool for forming the caulkedportions into contact with the ball during the caulking working.

In the production method described above, the pressure contact portionof the caulking tool comprises a plurality of continuous pressurecontact surfaces having different caulking angles, and when thesepressure contact surfaces are brought into pressure contact with theball point pen tip, a plurality of caulked portions having differentangles can be simultaneously formed in one production step. In thiscase, a first pressure contact surface of the pressure contact portionon the butt end side, which comes into contact with the outer surface ofthe distal butt end portion of the ball point pen tip, may be shapedinto a recessed curved surface.

The first pressure contact surface of the pressure contact portion onthe butt end side, which comes into contact with the outer surface ofthe distal end portion of the ball point pen tip, can be shaped into arecessed curved surface.

The reduced diameter portion for holding the ball under the state inwhich the ball protrudes partly from an inner hole portion of the ballpoint pen tip can be formed, too, by bringing the contact surface of arotary pressure contact member of caulking means into contact with amaterial while causing it to turn on its axis, rotating it round thematerial while a push deformation force is applied thereto, and movingthe contact surface towards the distal end open portion.

Further, the present invention provides a production method of a ballpoint pen tip which forms a reduced diameter portion by applyingcaulking to the distal end so that a ball as a writing member can beheld while partly protruding from an inner hole. This method can bepracticed by causing a fine granular member to impinge against at leastthe reduced diameter portion after the ball is held so as to changecorner portions into a curved surface.

The present invention further provides a production method of a ballpoint pen tip which forms a reduced diameter portion, and appliespolishing to the distal end portion of the ball point pen tip holdingthe ball placed in an inner hole so as to form the outer shape of thedistal end portion into a smooth curve, and this method can be practicedalso by connecting a synthetic resin pipe as an ink tank to the ballpoint pen tip, rotating this synthetic resin pipe while holding it so asto rotate the ball point pen tip, causing the synthetic resin pipe toundergo deflection, and then bringing a polishing material into contactwith the distal end portion for polishing under such a state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing the structure of a ball point pentip according to the first embodiment of the present invention.

FIG. 2 is an explanatory view showing a comparative example with thestructure of the ball point pen tip shown in FIG. 1.

FIG. 3 is a sectional view of principal portions, showing the structureof a ball point pen tip according to the second embodiment of thepresent invention.

FIG. 4 is an explanatory view showing the first example of theproduction method of the ball point pen tip according to the secondembodiment of the present invention.

FIG. 5 is an explanatory view showing the second example of theproduction method of the ball point pen tip according to the presentinvention.

FIGS. 6, 7 and 8 are views each showing a structural example of acaulking tool for practicing the production method of the ball point pentip according to the present invention.

FIGS. 9 and 10 are explanatory views each showing a method of polishinga distal end portion of the tip by rotating a synthetic resin pipehaving the ball point pen tip fitted thereto.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment will be explained with reference to thedrawings.

The ball point pen tip according to the first embodiment of the presentinvention has the following structure shown in FIG. 1:

(1) angle Y defined between a tangent L coming into contact with a ball8 and a body member or ball point pen tip A and a center line M of theball point pen tip is within the range of 30° to 50°;

(2) a corner portion 2a formed by caulking the ball point pen tip A (aboundary line between a portion at which a caulking tool and the tipcome into mutual contact and a portion at which they do not) and acorner portion 2c at the foremost distal end portion of the ball pointpen tip exist at portions other than the portion with which the tangentL of the ball point pen tip comes into contact; and

(3) the length of the portion F formed when a part near the opening ofthe inner surface of the ball point pen tip is brought into pressurecontact with the ball 8 at the time of caulking (an ink controlportion), in a longitudinal direction, is within the range of 15 to 35%of the ball diameter from an open end.

In contrast, FIG. 2 shows a Comparative Example wherein the cornerportion 2c at the foremost tip portion of the ball point pen tip existsat the portion with which the tangent L of the ball point pen tip comesinto contact.

In FIG. 1 described above, the structure (1) prevents the ball point pentip from coming into contact with the surface of a to-be-written objectsuch as the surface of a sheet when writing is made while the writinginstrument is kept inclined. When the degree of inclination of thewriting instrument main body is increased and the writing instrument islaid down, the ball point pen tip and the surface of the to-be-writtenobject come into mutual contact before long, but they do not come intomutual contact before the writing angle of 30° is reached. This angle isassociated with the projection height of the ball and the distance(clearance) between the tip opening and the ball. In other words, thegreater the projection height of the ball, or the smaller the distancebetween the tip opening and the ball, the smaller becomes the angle.

The structure (2) is to insure smooth feel of writing even when the tipA comes into contact with the surface of the to-be-written object duringwriting. When caulking is made, a corner is unavoidably formed in manycases at the boundary between the portion at which the caulking toolcomes into contact-with the tip and the portion at which they do not.Generally, the side surface of the ball point pen tip is shaped in sucha fashion that the diameter progressively decreases in multiple stagesand even when the reduction of the diameter is great, the corner doesnot have an acute angle. Nonetheless, however obtuse this angle may be,catch will occur once the surface of the to-be-written object and thecorner portion come into mutual contact. It is therefore necessary toavoid the formation of any portion which might result in catch, atportions of the ball point pen which have the possibility of coming intocontact with the surface of the to-be-written object.

Next, the structure (3) means that the smooth feel of writing can beaccomplished by mere prevention of catch on the surface of theto-be-written object but smooth rotation of the ball is indispensable.The ink control portion F described above is the portion which is formedwhen the inner wall of the ball point pen tip is pushed against the ball8 at the time of caulking of the ball point pen tip, provides a uniformclearance from the ball and has a shape substantially similar to theshape of the ball. In practice, however, the shape is not completelysimilar because so-called "return" due to plastic machining of ametallic material (so-called "spring-back") is not uniform, but acurvature substantially approximate to an arcuate shape can be obtained.

When contact between the inner wall of the ball holding chamber 7 of theball point pen tip and the ball is established by direct contact ofmetals, the frictional resistance becomes so great that the rotation ofthe ball is impeded. The ink existing inside the ball holding chamber 7of the ball point pen tip plays the role of a lubricant for assistingthe rotation of the ball, too, and to this end, an ink film must beformed over a certain area between the ball 8 and the inner wall of theball holding chamber inside the ball holding chamber 7.

In order to form this ink film, it is necessary to prevent the ball andthe inner wall of the ball holding chamber from coming into point orlinear contact (or to bring them into surface contact), or the ink musthave certain binding force (viscosity, tackiness, etc).

The ink control portion F is the portion at which the capillary force ishigh inside the ball holding chamber 7 and is the portion at which theink always exists and at which the ink film is formed. The formation ofa wide ink film in such a manner as to peripherally extend into thelength of 15 to 35% of the ball diameter from the open end of the tipmeans that the ink control portion F is formed up to the position in thevicinity of the center of the ball, though this depends on theprojection height of the ball. According to the experiments (WritingTest 1 in Tables 1A and 1B and Writing Test 2 in Tables 2A and 2B)listed below, a satisfactory lubrication effect cannot be obtained whenthe numerical value described above is smaller than 15%; and freemovement of the ink is impeded, on the contrary, and the ink cannot bespread over the entire surface of the ball when the numerical value isgreater than 35% (because a space like an ink reservoir exists to acertain extent inside the ball holding chamber).

In the Comparative Example shown in FIG. 2, catch with the surface ofthe sheet occurs and the writing resistance becomes greater than thesample shown in FIG. 1.

To evidence the range of the numerical value, ball point pen tipsfalling within this range and outside the range were produced, andwriting tests were carried out. The results were as follows. WritingTest 1 (structure shown in FIG. 1):

Testing Condition

machine used: line writing tester

(custom order product)

writing load: 200 g

writing speed: 7 cm/s

writing angle: 40°

writing instrument used:

K105 (a product of Pentel K.K.)

ball diameter: 0.7 mm

Corner was not formed at a contact point between tangent and ball pointpen tip (see FIG. 1).

The writing resistance value (g) under the writing condition describedabove was measured.

                  TABLE 1A                                                        ______________________________________                                        ink control portion (%)                                                                       5.7    10.0     15.7 20.0                                     length (mm)     0.04   0.07     0.11 0.14                                     tangent angle (°)                                                      20°      50     48       47   47                                       30°      45     40       30   28                                       40°      47     41       30   29                                       50°      48     42       35   34                                       60°      -*1    -*1      -*1  -*1                                      70°      -*1    -*1      -*1  -*1                                      ______________________________________                                    

                  TABLE 1B                                                        ______________________________________                                        ink control portion (%)                                                                       25.7   30.0     34.3 40.0                                     length (mm)     0.18   0.21     0.24 0.28                                     tangent angle (°)                                                      20°      61*2   62*2     62*2 63*2                                     30°      27     26       26   40*2                                     40°      28     27       27   42*2                                     50°      33     32       32   44*2                                     60°      -*1    -*1      -*1  -*1                                      70°      -*1    -*1      -*1  -*1                                      ______________________________________                                    

Writing Test 2 (Structure of Comparative Example shown in FIG. 2):

Testing Condition:

machine used: line writing tester (custom order product)

writing load: 200 g

writing speed: 7 cm/s

writing angle: 40°

writing instrument used:

K105 (a product of Pentel K.K.) ball diameter: 0.7 mm

The structure wherein corner was positioned at contact point betweentangent and ball point pen tip (se.e FIG. 2).

The writing resistance value (g) under the writing condition describedabove was measured.

                  TABLE 2A                                                        ______________________________________                                        ink control portion (%)                                                                       5.7    10.0     15.7 20.0                                     length (mm)     0.04   0.07     0.11 0.14                                     tangent angle (°)                                                      20°      52     48       50   60*2                                     30°      48     43       33   31                                       40°      63     56       45   44                                       50°      68     62       56   54                                       60°      -*1    -*1      -*1  -*1                                      70°      -*1    -*1      -*1  -*1                                      ______________________________________                                    

                  TABLE 2B                                                        ______________________________________                                        ink control portion (%)                                                                       25.7   30.0     34.3 40.0                                     length (mm)     0.18   0.21     0.24 0.28                                     tangent angle (°)                                                      20°      62*2   62*2     63*2 63*2                                     30°      30     29       29   41*2                                     40°      43     42       42   57*2                                     50°      53     53       52   65*2                                     60°      -*1    -*1      -*1  -*1                                      70°      -*1    -*1      -*1  -*1                                      ______________________________________                                    

Next, the structure of the ball point pen tip according to anotherembodiment of the present invention will be explained.

As shown in FIG. 3 which is a sectional view of principal portion of theball point pen tip A of the present invention, the ball point pen tip Ahas a taper surface 1 the diameter of which progressively decreasestowards the distal end thereof (upward in the drawing), and a reduceddiameter portion 2 is formed by caulking inward the distal end of thistaper surface 1. An ink passage 3 is formed as a connection hole insidethe ball point pen tip A. A center hole 5 whose diameter is reduced by aplurality of inward projection portions 4 and which has a ball receivingseat portion 4a and ink grooves 6 are formed in the ink passage 3. Thecenter hole 5 and the ink grooves 6 are open to the ball holding chamber7 defined by the inward projection portions 4. The ball 8 is held by theball holding chamber 7 and is prevented from jumping out by the reduceddiameter portion 2. The distal end portion of the ball 8 protrudes fromthe tip open portion 9 of the reduced diameter portion 2. The projectiondistance h of the ball from the tip open portion 9 is the exposed heightof the ball 8.

The reduced diameter portion 2 has two kinds of caulked portions havingmutually different caulking angles. They are a first caulked portion 2aon the distal end side and a second caulked portion 2b continuing fromthis first caulked portion 2a. The taper angle γ (the angle of diameterreduction of the taper surface) of the taper surface 1, the caulkingangle α of the first caulked portion 2a and the caulking angle β of thesecond caulked portion 2b are so set as to satisfy the relations,γ+10°≦β≦γ+40° and β+10°≦α≦β+40°. When γ and α are substantially 0°≦γ andα<180°, α, β, and γ satisfy the relations, 20°≦α<180°, 10°≦β<140° and0°≦γ100°. The ball point pen tip A shown in the drawing has α=about 80°,β=about 50°, γ=about 30°, h=about 0.200 mm, D=about 0.7 mm and t=about0.020 mm.

The ink control portion 10 which corresponds to the reduced diameterportion 2 of the ball holding chamber 7 is the portion which is pushedagainst the ball 8 at the time of caulking and is peripherally formed.It is smooth and has a uniform clearance from the ball. Because this inkcontrol portion 10 is smooth, ink movement becomes easy and ink can beeasily applied to, and carried by, the ball. Because the ink controlportion 10 has a uniform clearance from the ball 8, the quantity of inkcarried by the ball and discharged to the surface of the to-be- writtenobject becomes uniform, and density of written characters and uniformityof the writing width can be improved.

Here, ball point pen tips are produced by setting the caulking angle andthe diameter reduction angles α, β, γ of the taper surface and thedistance t between the outer shape of the small mouth portion at thedistal end of the opening and the outer shape of the ball to variousvalues, and catch of the tip to the surface of the to-be-written object(Test 1) and the density of written characters (Test 2) are tested forthese ball point pen tips at a writing angle of 40°. Incidentally, as tothe t value, samples having α=80°, β=50°, γ=30° are produced and Tests 1and 2 are carried out. The results are shown in Table 1 to Table 17. Theball point pen tips used for the tests have diameter reduction angles of30° and 35° for the taper surface, and the caulking angle at whichmachining was impossible is represented by symbol "-".

The production method of the ball point pen tip used for the tests is asfollows. First, the taper surface A of the ball point pen tip, the ballholding chamber 7 and the ink passage 3 are formed by cutting, or thelike. The ink passage 3 is formed with the center hole 5 and the inkgroove 6 in such a manner as to leave the inward projection portion 4,and then the ball 8 is loaded into the ball holding chamber 7. To holdthis ball 8, the reduced diameter portion 2 at the distal end of theball point pen tip A is formed by caulking.

Test 1! (Catch test to the surface at writing angle 40°)

The writing test was carried out under the following test condition andcatch between the ball point pen tip and the sheet surface was examined.

Evaluation:

◯: No contact was made between ball point pen tip and sheet surface.

Δ: Contact existed between ball point pen tip and sheet surface andwriting could be made, though friction sound occurs.

x: Ball point pen tip scratched sheet surface and uniform written linecould not be obtained.

Test 2! (Density test of written characters)

The writing test was carried out under the following test conditions andthe number of occurrences of density change of written characters wascounted.

Test Condition:

writing angle: 40°

vertical writing load: 200 g

writing distance: 100 m

tester used: spiral writing tester (Seiki Kogyo Lab.)

test sheet used: NS55 recording sheet (K.K. Kubishi KagakukikaiSeisakusho)

writing instrument used: BK100 (oily ball point pen, Pentel K.K.)

tip material: ferrite stainless steel

tip dimension: ball diameter 0.7 mm, ball projection height 0.200 mm

                  TABLE 3                                                         ______________________________________                                        γ (°)                                                                    30                                                                    α (°)                                                                    30                                                                    β (°)                                                                     30    40      50  60    70  80    90  100                             Test 1  --    --      --  --    --  --    --  --                              Test 2  --    --      --  --    --  --    --  --                              ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        γ (°)                                                                    30                                                                    α (°)                                                                    40                                                                    β (°)                                                                     30    40      50  60    70  80    90  100                             Test 1  --    x       --  --    --  --    --  --                              Test 2  --    23      --  --    --  --    --  --                              ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        γ (°)                                                                    30                                                                    α (°)                                                                    50                                                                    β (°)                                                                     30    40      50  60    70  80    90  100                             Test 1  --    .increment.                                                                           x   --    --  --    --  --                              Test 2  --    5       24  --    --  --    --  --                              ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        γ (°)                                                                    30                                                                    α (°)                                                                    60                                                                    β (°)                                                                     30    40      50  60    70  80    90  100                             Test 1  --    ∘                                                                         ∘                                                                     .increment.                                                                         --  --    --  --                              Test 2  --    0       0   7     --  --    --  --                              ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        γ (°)                                                                    30                                                                    α (°)                                                                    70                                                                    β (°)                                                                     30    40      50  60    70  80    90  100                             Test 1  --    ∘                                                                         ∘                                                                     ∘                                                                       ∘                                                                     --    --  --                              Test 2  --    0       0   3     6   --    --  --                              ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        γ (°)                                                                    30                                                                    α (°)                                                                    80                                                                    β (°)                                                                     30    40      50  60    70  80    90  100                             Test 1  --    ∘                                                                         ∘                                                                     ∘                                                                       ∘                                                                     ∘                                                                       --  --                              Test 2  --    5       0   0     4   12    --  --                              ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        γ (°)                                                                    30                                                                    α (°)                                                                    90                                                                    β (°)                                                                     30    40      50  60    70  80    90  100                             Test 1  --    .increment.                                                                           ∘                                                                     ∘                                                                       ∘                                                                     .increment.                                                                         x   --                              Test 2  --    8       2   0     0   10    45  --                              ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        γ (°)                                                                     30                                                                   α (°)                                                                    100                                                                   β (°)                                                                     30    40      50  60    70  80    90  100                             Test 1  --    x       .increment.                                                                       ∘                                                                       ∘                                                                     .increment.                                                                         .increment.                                                                       --                              Test 2  --    25      9   5     2   12    26  53                              ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                        γ (°)                                                                    35                                                                    α (°)                                                                    30                                                                    β (°)                                                                     30    40      50  60    70  80    90  100                             Test 1  --    --      --  --    --  --    --  --                              Test 2  --    --      --  --    --  --    --  --                              ______________________________________                                    

                  TABLE 12                                                        ______________________________________                                               γ(°)                                                             35                                                                            α(°)                                                             40                                                                            β(°)                                                                30    40      50  60    70  80    90  100                            ______________________________________                                        Test 1   --    x       --  --    --  --    --  --                             Test 2   --    35      --  --    --  --    --  --                             ______________________________________                                    

                  TABLE 13                                                        ______________________________________                                               γ(°)                                                             35                                                                            α(°)                                                             50                                                                            β(°)                                                                30    40      50  60    70  80    90  100                            ______________________________________                                        Test 1   --    Δ x   --    --  --    --  --                             Test 2   --    11      24  --    --  --    --  --                             ______________________________________                                    

                  TABLE 14                                                        ______________________________________                                               γ(°)                                                             35                                                                            α(°)                                                             60                                                                            β(°)                                                                30    40      50  60    70  80    90  100                            ______________________________________                                        Test 1   --    ◯                                                                         ◯                                                                     Δ                                                                             --  --    --  --                             Test 2   --     9       3  12    --  --    --  --                             ______________________________________                                    

                  TABLE 15                                                        ______________________________________                                               γ(°)                                                             35                                                                            α(°)                                                             70                                                                            β(°)                                                                30    40      50  60    70  80    90  100                            ______________________________________                                        Test 1   --    ◯                                                                         ◯                                                                     ◯                                                                       ◯                                                                     --    --  --                             Test 2   --     6       0   1    16  --    --  --                             ______________________________________                                    

                  TABLE 16                                                        ______________________________________                                               γ(°)                                                             35                                                                            α(°)                                                             80                                                                            β(°)                                                                30    40      50  60    70  80    90  100                            ______________________________________                                        Test 1   --    ◯                                                                         ◯                                                                     ◯                                                                       ◯                                                                     ◯                                                                       --  --                             Test 2   --     7       0   0     2  22    --  --                             ______________________________________                                    

                  TABLE 17                                                        ______________________________________                                               γ(°)                                                             35                                                                            α(°)                                                             90                                                                            β(°)                                                                30    40      50  60    70  80    90  100                            ______________________________________                                        Test 1   --    Δ ◯                                                                     ◯                                                                       ◯                                                                     Δ                                                                             x   --                             Test 2   --     8       1   0     0  16    50  --                             ______________________________________                                    

                  TABLE 18                                                        ______________________________________                                               γ(°)                                                             35                                                                            α(°)                                                             100                                                                           β(°)                                                                30    40      50  60    70  80    90  100                            ______________________________________                                        Test 1   --    x       Δ                                                                           ◯                                                                       ◯                                                                     ◯                                                                       Δ                                                                           x                              Test 2   --    28       7   0     2  12    28   57                            ______________________________________                                    

                  TABLE 19                                                        ______________________________________                                                γ(°)                                                             80                                                                            α(°)                                                             50                                                                            t(μm)                                                                         5    7         10  20      30  35                                  ______________________________________                                        Test 1    ◯                                                                       ◯                                                                           ◯                                                                     ◯                                                                         Δ                                                                           x                                   Test 2    15    0          0   0       3  23                                  ______________________________________                                    

The ball point pen tip according to the present invention does not causecatch with the written surface at a small writing angle and can obtainbeautiful written characters having a uniform density.

FIG. 4 is an explanatory view showing a production method of a ballpoint pen tip according to the present invention. First, the side walltaper surface 1 of the body member or ball point pent tip A, the ballholding portion or chamber 7 for accommodating the ball 8, the inkpassage 3 for passing ink to the ball holding chamber 7 and the centerhole 5 are formed, and then the ball 8 is loaded into the ball holdingchamber 7. Next, to hold this ball 8, the butt end portion 2 of the ballpoint pen tip A is caulked so as to form the caulked portions 2a, 2b.

A pressure contact portion 18 of the caulking tool or apparatus C whichcomes into contact with the ball point pen tip A includes a firstpressure contact surface 18a for forming the first caulked portion 2anear the butt end portion 2 of the ball point pen tip A and a secondpressure contact portion 18b so formed as to continue from the firstpressure contact surface at a different caulking angle from the firstpressure contact surface. The first pressure contact surface 18a isshaped in such a manner that a part of its extension comes into contactwith the ball 8, and machining of the caulked portion 2 is completed atthe position at which the first pressure contact surface 18a comes intocontact with the ball 8.

Because the caulking apparatus C applies caulking so that the pressurecontact surface of the pressure contact portion 18 comes into contactwith the ball, the end point of caulking is constant but does not vary.In other words, because the caulking angle and the size of the caulkedportion do not fluctuate, production can be stably carried out. Becausethe first caulked portion 2a and the second caulked portion 2b areformed by the continuous pressure contact surfaces 18a and 18b,protrusions as non-uniform wall thickness portions and fins (not shown)are not formed at the boundary portion of the caulked portions havingdifferent caulking angles.

Here, the caulking angle of the pressure contact surface is preferablyset, as shown in FIG. 4, so that the caulking angle α of the firstpressure contact surface 18a forming the first caulked portion, thecaulking angle β of the second pressure contact surface 18b and thetaper angler γ of the side wall taper surface of the ball point pen tipA other than the caulked portion 2 satisfy the relations, γ+10°≦β≦γ+30°and β+10°≦α≦β+30°.

The number of occurrences of "hollowed writing" (the phenomenon in whichportions not applied with ink occur during writing) is examined for theball point pen tips wherein the first caulked portion 2a and the secondcaulked portion 2b are formed in one production step and for the ballpoint pen tips wherein they are formed in two separate production steps(Test 1). The results are tabulated in Table 20.

                  TABLE 20                                                        ______________________________________                                                 angle α                                                                 60°   70°                                                                           80°                                                angle β                                                                  40°  50°                                               ______________________________________                                        one step   12            11     12                                            two steps  40            55     68                                            ______________________________________                                    

Test Condition:

writing angle: 70°

vertical writing load: 200 g

writing distance: 200 m

tester used: Spiral writing tester (Seiki Kogyo Lab)

test sheet used: NS55 recording sheet (K.K. Kubishi KagakukikaiSeisakusho)

writing instrument used: BK 100 (oily ball point pen, Pentel K.K.)

tip material: ferrite stainless steel

tip dimension: ball diameter 0.7 mm, ball projection height 0.21 mm,taper angle (β) of tip side portion 30°

The relation between the first caulking angle α and the second caulkingangle β is examined by an oblique writing test (Test 2). The results aretabulated in Table 21.

                  TABLE 21                                                        ______________________________________                                                      β = 40°                                                                 β = 50°                                       ______________________________________                                        α = 50°                                                                          ◯                                                                         --                                                    α = 60°                                                                          ◯                                                                         ◯                                         α = 70°                                                                          ◯                                                                         ◯                                         α = 80°                                                                          x       ◯                                         α = 85°                                                                          x       x                                                     ______________________________________                                    

Test Condition:

writing angle: 45°

vertical writing load: 200 g

writing distance: 200 m

tester used: Spiral writing tester (K.K. Kubishi Kagakukikai Seisakusho)

test sheet used: NS55 recording sheet (K.K. Kubishi KagakukikaiSeisakusho)

writing instrument used: BK 100 (oily ball point pen, Pentel K.K.)

tip material: ferrite stainless steel

tip dimension: ball diameter 0.7 mm, ball projection height 0.21 mm,taper angle (γ) of tip side portion 30°

Evaluation:

◯: uniform and continuous writing distance of at least 50 m

x: uniform and continuous writing distance of 0 to less than 50 m

FIG. 5 shows the production method according to another embodiment ofthe present invention. This embodiment is fundamentally the same as theembodiment shown in FIG. 2 but is different in that the first caulkedportion 2a has a curvature. An increase in the caulking angle of thefirst pressure contact surface 18a forming the first caulked portiondecreases the space between the ball 8 and the butt end portion 2.Therefore, the pressure contact surface is shaped into a recessed curvedsurface. In the example shown in the drawing, the first caulked portion2a has a curved surface having a radius 5 to 30% of the diameter of theball 8. With this arrangement, the contact between the ball point pentip and the written surface becomes smooth during writing. The "hollowedwriting" phenomenon can be reduced to minimum by reducing the spacebetween the ball 8 and the butt end portion 2. In other words, one ofthe causes for the occurrence of this "hollowed writing phenomenon" isair entering the ball point pen tip due to the rotation of the ball 8,and when the space between the ball 8 and the butt end portion 2 isreduced to minimum, air is not likely to enter the ball point pen tipand the "hollowed writing phenomenon" can be minimized.

As shown in the drawing, the caulking angle of the pressure contactsurface is preferably set so that the caulking angle β of the secondpressure contact surface 18b and the taper angle γ of the side walltaper surface of the ball point pen tip A other than the caulked portion2 satisfy the relation, γ+10°≦β≦γ+30°.

Various other modifications can be made besides the example describedabove. For example, diameter reduction machining can be made in advanceto some extents before caulking in order to minimize the load to thetool, and not only the first pressure contact surface 18a but also thesecond pressure contact surface 18b can be shaped into the curvedsurface. A so-called "pipe type ball point pen" wherein the inkcommunication groove 6 and the center hole 5 are formed by pressing ametallic pipe can be used for the ball point pen tip.

The number of occurrences of the "hollowed writing phenomenon" isexamined for the ball point pen tips whose first caulked portion 2a hasa curved surface (Test 3). The results are tabulated in Tables 22 and23.

                  TABLE 22                                                        ______________________________________                                        1      0.02   0.05      0.10 0.20   0.25 0.30                                 2      2.8    7.1       14.3 28.6   35.6 42.8                                 β 40°                                                             3      16     7         8    12     18   23                                   4      51     27        35   40     54   65                                   ______________________________________                                         1 radius of curved surface (mm)                                               2 proportion of radius of curvature to ball diameter (%) = radius of          curved surface (mm) × 100/ball diameter (mm)                            3 one production step                                                         4 two production steps                                                   

Test Condition:

writing angle: 70°

vertical writing load: 200 g

writing distance: 200 m

tester used: Spiral writing tester (Seiki Kogyo Lab)

test sheet used: NS55 recording sheet (K.K. Kubishi KagakukikaiSeisakusho)

writing instrument used: BK100 (oily ball point pen, Pentel K.K.)

tip material: ferrite stainless steel

tip dimension: ball diameter 0.7 mm, ball projection height 0.21 mm,taper angle (γ) of tip side portion

                  TABLE 23                                                        ______________________________________                                        1      0.02   0.05      0.10 0.20   0.25 0.30                                 2      2.8    7.1       14.3 28.6   35.6 42.8                                 β 50°                                                             3      14     5         7    10     15   20                                   4      48     26        32   38     52   63                                   ______________________________________                                         1 radius of curved surface (mm)                                               2 proportion of radius of curvature to ball diameter (%) = radius of          curved surface (mm) × 100/ball diameter (mm)                            3 one production step                                                         4 two production steps                                                   

Test Condition:

writing angle: 70°

vertical writing load: 200 g

writing distance: 200 m

tester used: Spiral writing tester (Seiki Kogyo Lab)

test sheet used: NS55 recording sheet (K.K. Kubishi KagakukikaiSeisakusho)

writing instrument used: BK 100 (oily ball point pen, Pental K.K.)

tip material: ferrite stainless steel

tip dimension: ball diameter 0.7 mm, ball projection height 0.21 mm,taper angle (γ) of tip side portion 30°

The production method of the ball point pen tip according to the presentinvention described above limits the complicated work and can producethe ball point pen tip having excellent writing feel and writingquality.

FIGS. 6 and 7 are sectional view of the principal portions when caulkingis applied to the ball point pen tip A by using a preferred caulkingtool C. FIG. 6 shows the start point of caulking and FIG. 7 shows itsend point.

The caulking tool C described above has a rotary pressure contact member21 which rotates at the center of a rotary shaft 22. The rotary shaft 22is fitted, through a spring 23 as a flexible member for absorbing anexcessive push force, to a holder 24 connected to a position movementcontroller (not shown). A pressure contact portion 21a of the rotarypressure contact member 21 is moved in a direction of the tip openportion 9 of the ball point pen tip A (in the direction indicated by anarrow in FIG. 6) while being rotated round the ball point pen tip A (seeFIG. 7). The smaller the width of this pressure contact portion 21a, theless frequent is the occurrence of the stress to the push position andthe greater becomes an escape portion of the resulting stress. However,because the distance to the tip open portion 9 becomes great in thiscase, the width is preferably 5 to about 30% of the width of the portionto be caulked.

FIG. 8 shows still another embodiment, and depicts the end point ofmachining corresponding to FIG. 7. The differences of this embodimentfrom the embodiments shown in FIGS. 5 and 7 are that the contact portionwith the ball point pen tip is provided with a gradual curved surface bychanging the shape of the rotary push member and that the shape of thetip open portion 9 before machining is different. Besides the metal, arubber, a synthetic resin, ceramics, etc, can be used as the material ofthe rotary push member 22, and the shape need not be changed inaccordance with the material. However, when a relatively soft materialsuch as the rubber or the synthetic resin is selected, the thickness ofthe tip open portion 9 of the ball point pen tip A is preferably reducedbefore machining as shown in FIG. 8. If the thickness is great for thissoft material, the load to the thick portion 22 becomes great andservice life of the tool might be relatively reduced.

As a modified embodiment of this embodiment, a plurality of rotary pushmembers may be simultaneously brought into contact with the ball pointpen tip, or the push force of the rotary push member may be kept at aconstant value as a whole but is changed in accordance with the contactposition. The ball point pen may be a ball point pen of a type (pipetype ball point pen) wherein a part of the side portion of a pipe memberis deformed so as to form an inward projection portion and the ball isplaced at this projection portion.

In the various production methods of the ball point pen tip describedabove, the corner portions can be shaped into a curvature shape bycausing fine granules to impinge against at least the reduced diameterportion 2 after the ball 8 is held. Such an embodiment will bedescribed.

In other words, a blank having a reduced diameter portion formed by acaulking tool and holding a ball is put into a hexagonal prismaticsample pot of a centrifugal fluidization barrel (model HS-1-4V, aproduct of Tipton Espo K.K.) with SF-8D (pulverized corn seed with anaverage particle diameter of about 1.5 mm) as a fine granular grindingmaterial and with chromium oxide powder (average grain size 3 μm) forgrinding, a product of Tipton Espo K.K., and is treated for 3 hours at280 rpm with a radius of rotation of 120 mm .

The blank to be treated has a ball of a cemented carbide having a balldiameter of about 0.7 mm, a diameter reduction angle of about 30° at thetaper portion, a caulking angle of about 80° at the distal end side, acaulking angle of about 52° on the reduced diameter side, a ballprojection distance of the ball of about 0.2 mm from the open portionand a thickness of about 0.01 mm at the tip distal end. The finegranular member consisting of SF-8D put into the sample pot with theblank should account for 30 to 70% of the pot volume per 100 to 500blanks, and 50% of SF-8D is put in this example. Though the volume ofchromium oxide powder for grinding is preferably from 1 to 10%, thisexample uses a volume of 5%.

As the fine granular member and the blank are rapidly stirred inside thesample pot, the fine granular member uniformly impinges against thesurface of the blank, and the corner portions on the blank surface areground and/or deformed into the curved surface shape. In this case,composite powder of chromium oxide power for grinding and SF-8Dapparently forms one grinding particle with SF-8D being the base. Afterthis treatment, the surface of the ball point pen tip A so obtained hasa mirror surface, and does not easily cause catch on the written surfacesuch as a paper surface in writing. Moreover, it can provide highquality appearance. In addition to the distal end portion, the cornerportions (not shown) at the rear end of the step portion between thelarge diameter portion and the reduced diameter portion can be shapedinto the curved surface, as well, and the surface of the reduced portionas the joint portion with the ink tank (not shown) can be shaped intothe mirror surface. Therefore, the problem of ink leakage, too, can beminimized.

Incidentally, since chromium oxide used as the fine granular memberlocally attains a high temperature and a high pressure at the machinedportion, it is under the state of metallic chromium and chromium ions.This chromium diffuses into the stainless materials, increases thequantity of chromium on the surface and improves corrosion- andwear-resistance. Generally, those alloys which have a large chromiumcontent have low cuttability and for this reason, it has been difficultto form a ball point pen tip by using materials having a high chromiumcontent from the beginning. However, the production method of thisembodiment can obtain a ball point pen tip having excellent corrosion-and wear- resistance.

The combination of the granular members used is not limited to theexample given above. For example, SF-14 (pulverized) walnut shells withan average particle size of about 1.2 mm), a product of Tipton EspoK.K., may be used in place of SF-8D of Tipton Espo K.K., and chromiumnitride powder and chromium carbide powder may be used in place ofchromium oxide powder. Though the radius of rotation for rotating thesample pot is suitably from 100 to about 200 mm, the number ofrevolutions may be suitably set in accordance with the radius ofrotation. The number of revolutions is preferably within the range of100 to 400 rpm. Further, the treatment time is from 10 to 300 minutes.When brass or german silver is used as the material, however, thetreatment time is preferably from 10 to 30 minutes.

Another example will be given.

This example uses the same blank as the one used in the exampledescribed above, and two kinds of silicon carbide powder having particlesizes of 1.5 mm and 1.2 μm, as the grinding agent. These blank andgrinding agent are put into the sample pot of the centrifugalfluidization barrel with cooling water and a surfactant (Model LC-2, aproduct of Tipton Espo K.K.) for removing dust of the blank, andtreatment is carried out at 220 rpm for 30 minutes with a radius ofrotation of 170 mm, in the same way as in the example given above.

In the same way as in the example given above, 50% of silicon carbidepowder having a particle size of 1.5 mm per 100 to 500 blanks, in termsof the volume of the sample pot, and 5% of silicon carbide powder havinga particle size of 1.2 μm are put into the sample pot, and 600 cc ofcooling water and 10 ml of the surfactant (Model LC-2) are added.

Since this example uses silicon carbide powder having a large particlesize of 1.5 mm and a relatively large mass, a relatively strong impactforce can be applied to the blank surface. Great work hardening of thematerial occurs at the distal end portion having a large machiningratio, and a ball point pen tip having excellent durability can beobtained.

Still another example will be explained.

This example uses the same blank as those of the foregoing examples, anda ball point pen tip is produced by using an apparatus which blasts thefine granular member with high pressure air to this blank. This exampleuses PNEUMA BLASTER SL-3, a product of Fuji Seisakusho K.K., andMorrundum A #1200 (silicon carbide powder, average particle size of 9.5μm), a product of Showa Denko K.K., as the fine granular member.

The blasting condition of the fine granular member to the portion of theblank corresponding to the tip butt end portion is as follows. The finegranular member is blasted at a jet air pressure of 3.5 kg/cm² at anangle of 45° from the longitudinal direction of the tip and from adistance of about 300 mm from the blank while the blank is rotatedonce/sec for about 5 seconds.

In the ball point pen tip obtained by this example, the corner portionson the blank surface are polished and/or deformed into the curvedsurface, and since a large number of fine concavo-convexities areformed, the surface condition has a so-called satin finished surface.

As described above, the production method of the ball point penaccording to the present invention can minimize the occurrence of catchof the corner portions 4 with the to-be-written object such as paperduring writing, can extremely stabilize ink discharge and can reduce theoccurrence of the so-called "hollowed writing phenomenon" and the"blurr".

Next, fine machining lines, scratches and fins are unavoidably formed atthe distal end portion of the ball point pen due to cutting for shapingthe outer shape and caulking. They cause catch with the surface of theto-be-written article such as the sheet surface and not only increasesthe frictional resistance at the time of writing but also scratches thesurface of the to-be-written object. Since ink permeates into thescratches, distortion of writing occurs. Therefore, it is desirable andnecessary to shape the outer shape of the ball point pen, particularlythe outer shape of the tip portion which is most likely to come intocontact with the written surface, into a smooth curve shape.

To accomplish this object, it has been customary to conduct so-called"polishing" by causing a polishing member obtained by applying a finepolishing material such as powder of chromium oxide or silicon carbideto a cloth such as a felt or cotton to move relatively while keepingcontact with the ball point pen tip surface.

In an embodiment of the present invention, the synthetic resin pipe usedas the ink tank is connected to the ball point pen tip, and is rotatedwhile it is held to rotate the tip so as to bring the polishing materialinto contact with the distal end portion at the position at which thesynthetic resin pipe undergoes deflection and to apply the polishingwork to the contact portion. In this way, even when the contact force ofthe polishing material coming into contact with the ball point pen tipis somewhat excessive, the excessive contact force can be absorbed bythe deflection of the synthetic resin pipe. The fine adjustment of thecontact force can be made easily and reliably by adjusting the holdingposition of the synthetic resin pipe and its distance from the polishingmaterial.

FIGS. 9 and 10 show an example where the synthetic resin pipe isdeflected and the polishing material is brought into contact with thedistal end portion, so as to apply polishing to the contact portion.

In FIG. 9, a grinder 34 having a rotating device 33 for rotating thesynthetic resin pipe 32 having the ball point pen tip A fitted theretoand a polishing material 34a for polishing the distal end portion of theball point pen tip A is used. The rotating device 33 includes a rubberroll 33a for imparting the rotating force to the synthetic resin pipe 32and a reception roller 33b, and the synthetic resin pipe 32 is heldbetween these rubber rollers 33a and reception roller 33b. In order tofacilitate the rotation of the synthetic resin pipe 32, protuberances orprojections are formed on the contact surface 33c of the rubber roller33a with the synthetic resin pipe 32 in a direction parallel to thelongitudinal direction of the synthetic resin pipe 32 so as to increasethe coefficient of friction. To prevent the contact surface 33c with thepipe 32 of the reception roller 33b from damaging the synthetic pipe 32,a synthetic resin sheet or a cloth may be bonded to the contact surface33c of the reception roller 33b or this roller 33b itself may be shapedfrom a synthetic resin.

The grinder 34 includes a grinding material 34a which rotates with arotary shaft 34b being the center and brings the polishing surface 34cat the side portion into contact with the material. The polishingsurface 34c is shaped from a cloth or a fiber bundle such as a felt anda cotton, or a leather, and when brought into contact with the ballpoint pen tip A while rotating, it removes corners, fine machininglines, scratches, fins, etc, formed on the outer shape of the ball pointpen tip A and shapes the outer shape into a smooth curved surface. Thepolishing effect can be improved by applying fine powder of chromiumoxide, silicon carbide, aluminum oxide, diamond, etc, to the polishingsurface 34c.

The contact position between the polishing material 34a and the ballpoint pen tip A is deviated from the position at which the rotatingdevice 33 holds the synthetic resin pipe 32. In this way, the syntheticresin pipe 32 is allowed to undergo deflection. This deflection quantitycan be adjusted by adjusting the distance between the holding positionof the synthetic resin pipe 32 by the rotating device 33 as the supportpoint and the contact portion of the polishing material 34a with theball-point pen A. In other words, this distance is increased when agreat deflection quantity is necessary, and is decreased when a smalldeflection quantity is necessary. Here, when the rotating direction ofthe polishing material 34a is set to the rotating direction R as shownin the drawing, the powder polishing material cannot easily enter theinner hole of the ball point pen tip; hence, this structure ispreferable.

Further, if the rotary shaft 34b is further deviated by 90° from theposition in FIG. 7 and polishing is conducted in the vertical directionwith respect to the longitudinal direction of the ball point pen tip Aas shown in FIG. 10, durability of the polishing material can beimproved and life becomes longer desirably.

What is claimed is:
 1. A ball point pen tip comprising: a body memberhaving a recess containing a ball, a caulked portion formed by acaulking tool for retaining the ball in the recess, first cornerportions disposed at a foremost end portion of the body member, andsecond corner portions defining a boundary between the caulked portionand a portion of the body member which is not contacted by the caulkingtool during formation of the caulked portion; wherein an angle definedbetween a tangential line coming into contact with both the ball and thebody member and a center line of the ball point pen tip is within therange of 30° to 50°, the tangential line coming into contact with thecaulked portion of the body member but not with the first and secondcorner portions thereof; and wherein the length of a portion of an innersurface of the recess from an opening thereof which is brought intopressure contact with the ball when the caulked portion is formed by thecaulking tool is within the range of 15% to 35% of a diameter of theball.
 2. A ball point pen tip according to claim 1; wherein the caulkedportion is disposed between the first and second corner portions.
 3. Aball point pen tip comprising: a distal end portion; a taper surfacehaving a diameter progressively decreasing towards the distal endportion; a reduced diameter portion formed by caulking the distal endportion inwardly and defining first and second caulked portions havingmutually different caulking angles; a ball holding portion; an inkpassage communicating with the ball holding portion; and a ball disposedin the ball holding portion and projecting outwardly from an openingthereof; wherein a caulking angle α of the first caulked portion, acaulking angle β of the second caulked portion, a diameter reductionangle γ of the taper surface, a diameter D of the ball, a projectionheight h of the ball from the opening of the ball holding portion, and adistance t between an outer surface of the distal end portion proximatethe opening of the ball holding portion and an outer surface of the ballsatisfy the following relations (1) to (4):

    0.25D≦h≦0.35D                                (1)

    0.007 mm≦t≦0.030 mm                          (2)

    γ+10°≦β≦+40°        (3)

    β+10°≦α≦β+40°  (4).


4. 4. A method of manufacturing a metallic ball point pen tip,comprising the steps of: providing a body member having a distal endportion and a ball holding portion; disposing a ball in the ball holdingportion; and forming a plurality of caulked portions having differentangles throughout the entire periphery of an outer surface of the distalend portion of the body member using a caulking tool while bringing apressure contact portion of the caulking tool into contact with theball.
 5. A manufacturing method according to claim 3; wherein thepressure contact portion of the caulking tool comprises a plurality ofcontinuous pressure contact surfaces having different caulking angles;and wherein the forming step includes bringing the pressure contactsurfaces into pressure contact with the ball point pen tip to form theplurality of caulked portions in a single process.
 6. A manufacturingmethod according to claim 5; wherein one of the pressure contactsurfaces of the pressure contact portion comprises a recessed curvedsurface; and wherein the forming step includes bringing the recessedcurved surface into contact with the distal end portion of the body. 7.A method of manufacturing a ball point pen tip, comprising the steps of:providing a body member having an open end at a distal end portionthereof and a recess containing a ball; bringing a contact surface of arotary pressure contact member of a caulking mechanism into contact withthe distal end portion of the body member while the pressure contactmember is allowed to rotate on its own axis around the body member; andimparting a pressing deformation force to the distal end portion of thebody member while moving the contact surface of the rotary pressurecontact member towards the open end of the body member to form a reduceddiameter portion around a periphery of the distal end portion forholding the ball in the recess so that the ball protrudes partially fromthe recess.
 8. A method of manufacturing a ball point pen tip,comprising the steps of: providing a body member having an open end at adistal end portion thereof and a recess containing a ball; pressing thedistal end portion of the body member to form a reduced diameter portionso that the ball is allowed to be retained in and partly protrude fromthe recess; and thereafter causing a fine granular member to impingeagainst at least the reduced diameter portion of the body member to formcorner portions having a curved surface.
 9. A method of manufacturing aball point pen tip, comprising the steps of: providing a body memberhaving a reduced diameter portion at a distal end thereof and a recesscontaining a ball; connecting the body member to a rotatable,deflectable synthetic resin pipe for rotation therewith; and polishingthe reduced diameter portion of the body member into a smooth curvedshape by bringing a polishing member into contact with the distal end ofthe body member while rotating the synthetic resin pipe and whileallowing the rotating synthetic pipe to deflect.
 10. A ball point tipfor use in a ball point pen, the ball point tip comprising: a tubularbody member having a first open end, a spherical ball retained in thefirst open end, a second open end opposite the first open end forreceiving writing fluid, and a wall having a caulked portion formed by acaulking tool for retaining the spherical ball in the first open end,the wall having first corner portions disposed at a foremost end portionof the tubular body member and second corner portions defining aboundary between the caulked portion and a portion of the tubular bodymember which is not contacted by the caulking tool during formation ofthe caulked portion; wherein an angle defined between a tangential linetangent to both the spherical ball and the wall and a center line of theball point tip is within the range of 30° to 50°, the tangential linecoming into contact with the caulked portion of the tubular body memberbut not with the first and second corner portions thereof.
 11. A ballpoint tip according to claim 10; wherein the caulked portion of the wallis formed by a caulking device while pressing an inner surface portionof the wall corresponding to the caulked portion into pressure contactwith the spherical ball; and wherein the length of the inner surfaceportion of the wall from the first open end thereof which is pressedinto pressure contact with the spherical ball is within the range of 15%to 35% of a diameter of the spherical ball.
 12. A ball point tipaccording to claim 10; wherein the caulked portion is disposed betweenthe first and second corner portions.
 13. A method of manufacturing aball point tip of a ball point pen, comprising the steps of: providing atubular body member having a ball holding portion at a first open endthereof, a spherical ball disposed in the ball holding portion, and asecond open end opposite the first open end for receiving writing fluid;and pressing a portion of the tubular body member proximate the firstopen end using a caulking device while bringing a pressure contactportion of the caulking device into contact with the spherical ball toform a plurality of caulked portions for retaining the spherical ball inthe ball holding portion.
 14. A manufacturing method according to claim13; wherein the pressure contact portion of the caulking devicecomprises a plurality of continuous pressure contact surfaces havingdifferent caulking angles; and wherein the pressing step comprisesbringing the pressure contact surfaces of the caulking device intopressure contact with the portion of the tubular body member to form theplurality of caulked portions having different caulking angles.
 15. Amanufacturing method according to claim 14; wherein one of the pressurecontact surfaces of the caulking device comprises a recessed curvedsurface; and wherein the pressing step comprises bringing the recessedcurved surface into contact with the portion of the tubular body member.